The present invention relates generally to the correction of vision by insertion of a corrective element into the eye, and more precisely the correction of presbyopia.
It will be recalled that, as shown in FIG. 1, the lens Cr enclosed in the lens sac S is suspended from the ciliary body Cc by means of the zonule Z. This ciliary body Cc lines the internal surface of the sclera about a ring located on the average at a latitude distant by 2 to 3 mm from the limbus, measured along the optical axis.
Presbyopia is a loss or reduction of the accommodating power of the eye which takes place when the person ages.
According to a theory of about a hundred years ago, Von Helmholtz explained the physiology of the accommodation of near vision by a relaxation of the zonule tension exerted on the lens during contraction of the ciliary body. This relaxation of tension gives rise to the lens taking a more globular form having smaller radii of curvature and hence more convergent as to the focal point. At the same time, the lens move forward in an antero-posterior plane.
Schachar proposed beginning in 1992, particularly in his U.S. Pat. Nos. 5,354,331, 5,465,737, 5,489,299 and 6,007,578, a theory contrary to that of Von Helmholtz, according to which the accommodation was due to a tensile force exerted on the lens when the ciliary body relaxes, such a force tensioning the zonule ligament which creates a flattening of the periphery of the lens and a convex projection of the center of the latter.
Moreover, according to Schachar, the diameter of the lens increases in the course of aging and the distance separating the periphery of the lens from the ciliary body diminishes bit by bit, which leads to a relaxation of the zonule. As a result, the centrifugal effort exerted by the ciliary body on the periphery of the lens is no longer sufficiently great to ensure the accommodation.
Schachar proposed in the patents mentioned above, different methods permitting improving the accommodation power of an eye, consisting for example in surgically reducing the length of the zonules or the diameter of the lens, or preventing enlargement of the lens.
Another method of treatment proposed by Schachar has been very widely used. It consists in treating presbyopia by positioning a truncated conical ring about the scleral ring to create a sort of external suspension, so as to enlarge the diameter of the ciliary body and hence to restretch the zonule.
Such an intervention being fairly important, it has been proposed subsequently to position on the sclera arcuate scleral expansion segments, of a radius of curvature less than the radius of curvature of the sclera. These segments pass through passages encised in the surface of the sclera concentrically to the limbus, in line with the ciliary body, and bear with their ends on the external surface of the sclera.
In FR 98 12834 of the applicant, such segments have ends of spatulate form so as not to risk perforating the sclera at the points of bearing of the segment on the sclera and preventing turning of said segments.
It has been noted that the operations carried out since 1992 by following the Schachar theory have sometimes succeeded and permitted giving the patient good vision, but sometimes not, the accommodation not being really better after the intervention.
Moreover, in certain patients, the segments have been expelled from the sclera, after pulling out of the passages in which they were positioned.
As a result, the Schachar theory is not able to solve the problem of the treatment of presbyopia.
By analyzing the results of procedures practiced by specialists, the applicant as arrived at the conclusion that the Schachar theory was inexact even though its practice permitted in certain cases obtaining the desired result.
The applicant concluded that the correction of presbyopia observed in certain patients after implantation of a truncated conical ring or arcuate segments on the sclera would not do as Schachar thought, to an effect of traction exerted on the zonule and hence on the lens, but to an induced result obtained during the procedure without the operator seeking it.
The applicant has taken account of the fact that the eyeball has a flexible but inextensible surface and has concluded that it is not possible to increase the circumference of the scleral ring by exerting centrifugal tension at certain points on the sclera.
By examining in greater detail the procedures carried out according to the Schachar method, the applicant has determined that by exerting a centrifugal tension at certain points, the emplacement of segments of scleral expansion would exert as a reaction a centripetal pressure in line with their points of bearing on the sclera.
The applicant thus explains the observed effect with certain rings or scleral expansion segments, not by the traction that they exert on the zonule at certain points, but by the pressure that they exert on the latter at other points. When the pressure is exerted in line with the ciliary body, it artificially compensates the defect of contraction of said ciliary body and helps the eye in its accommodation work as was described by Von Helmholtz.
These observations led the applicant to provide by the present invention a corrective element permitting correcting presbyopia reproducibly and not at random, as in the procedures proposed for about the last ten years.
To this end, the invention relates to a corrective element permitting correcting presbyopia, adapted to be implanted in the eye in line with the ciliary body, characterized in that it is shaped to exert on said ciliary body a centripetal force directed perpendicularly to the optical axis.
This element is noteworthy in that it has, in cross-section, an external wall adapted to be disposed parallel to the surface of the sclera and an internal wall adapted to be disposed parallel to the optical axis of the eye.
The sclera being inextensible, such an element acts by bearing on the portion of the sclera which it covers to press the ciliary body in the direction of the optical axis of the eye and to form indentations in said ciliary body. As a result, centripetal forces on said ciliary body artificially compensate the loss of contraction of the latter and thus re-establish its action necessary for accommodation, which is to say the zonular relaxation.
The increase of the contractive force of the ciliary body with a decrease of the diameter of the ciliary ring by elements forming indentations in the ciliary body, permits relaxing the zonule and letting the lens profit from its residual flexibility to become more globular.
The corrective element according to the invention is all the more remarkable in that:
it is constituted by an arcuate segment whose radius of curvature is such that after its emplacement in the eye, said segment will be centered on the optical axis of said eye,
a rear wall connects the rear elongated ends to each other of said external and internal walls,
a rounded portion connects the concurrent front ends of said external and internal walls,
the angle comprised between the external wall and the internal wall is of the order of 45xc2x0,
the rear wall is rounded,
the rear wall is constituted by a portion of a torus.